Drift Volume Research Articles

Evaluation Method of Seismic Capability for Moment-Resisting Frames of Reinforced Concrete Structure-Reaction Modelling of Member Displacement

Story drift of structure is an important indication of structural damage subjected earthquake excitation. It is thus more reasonable to include base shear and story displacement volume in the assessment of seismic resistant capability of structure. The purpose of this study is to apply lateral displacement reaction model of structural member established through experiments as a base and put in use the derived relation between member deformation and story displacement of structure, integrated with the influence of dynamic p-Δ effect and the required consideration for the structure’s functionality, to evaluate earthquake proof capability of moment-resisting frames of reinforced concreté structure. This proposed evaluation method is indicated by the collapse ground acceleration and the extreme volume of story drift. To test the correctness and simplicity of this proposed method, example analysis can be employed and compared the proposed method with elastic static earthquake proof method, nonlinear dynamic analysis method and capacity spectrum method. The analysis outcome shows that the analysis results of proposed method are the nearest to the results of dynamic analysis, and this method is also the simplest and most accurate than the others.

TPG construction

TPG is the acronym for a 3D imaging gas chamber with GEM amplification, hexaboard read-out and FADC electronics. We have constructed a TPG-head with three GEM foils (30 cm diameter) and a read-out board (30 cm diameter active surface) covered with 710,000 hexagonal pads of 300μm size. Aligned pads are connected in parallel to one strip out of three sets of 576 parallel strips (500μm pitch). The three sets of strips run at 120∘ from each other and at three different depths inside the hexaboard multilayer structure. Each strip is read out by FADC electronics. The TPG-head is under initial test in a small container with a drift volume 33 mm long and of 30 cm diameter. A 150 cm long drift volume inside a 0.7 T solenoidal magnetic field has been prepared by using HARP-TPC instrumentation as test bed.

TPG construction

TPG is the acronym for a 3D imaging gas chamber with GEM amplification, hexaboard read-out and FADC electronics. We have constructed a TPG-head with three GEM foils (30 cm diameter) and a read-out board (30 cm diameter active surface) covered with 710,000 hexagonal pads of 300 μ m size. Aligned pads are connected in parallel to one strip out of three sets of 576 parallel strips ( 500 μ m pitch). The three sets of strips run at 120 ∘ from each other and at three different depths inside the hexaboard multilayer structure. Each strip is read out by FADC electronics. The TPG-head is under initial test in a small container with a drift volume 33 mm long and of 30 cm diameter. A 150 cm long drift volume inside a 0.7 T solenoidal magnetic field has been prepared by using HARP-TPC instrumentation as test bed.

Design and construction of a GEM-TPC prototype for research and development purposes

For a number of running and future particle-physics experiments, studies on the readout of time projection chambers (TPCs) based on the gas electron multiplier (GEM) are ongoing. This technology offers higher granularity and intrinsically suppressed ion feedback as the two major advantages compared to a conventional readout with multiwires. We describe the design and construction of a small and flexible TPC prototype, whose cylindrical drift volume can be equipped with endcaps of different gas detector types. Its field cage is designed in a double-ring layout to guarantee high homogeneity of the electric field. All materials facing the gas volume have been selected with special respect to detector aging properties. An endcap with multi-GEM readout is currently set up and successfully operated with a modified version of the STAR-TPC electronics. The functionality of the detector has been verified in system checks, and its performance could recently be tested in high-intensity particle beams.

Equilibrium and cross-sectional stability of tidal inlets: application to the Frisian Inlet before and after basin reduction

The focus of this paper is on the adaptation of the inlet cross-sectional area after basin reduction. To calculate the new equilibrium and degree of stability, use is made of a method first proposed by Escoffier. As part of this study his largely empirical approach is expanded and given a physical basis. The inlet channel is divided in an entrance and interior section. Sand enters the entrance section on the flood and is removed by the ebb tidal current. On annually average basis, the volume of sand entering the inlet is assumed to be a constant fraction of the littoral drift. A theoretical expression for the ebb tidal sand transport as a function of the tidal velocity amplitude and a length dimension of the cross-section is derived. An important ingredient in the stability analysis is the empirical cross-sectional area versus tidal prism relationship for inlets in equilibrium and the related equilibrium velocity. A physical justification for this relationship is presented. As a measure for cross-sectional stability, a stability index, S, is introduced. For S≥1, the inlet is very stable. Stability increases with increasing values of S. For inlets that are very stable, the value of S can be related to P/ V, i.e. the ratio of tidal prism and volume of littoral drift. A method to determine the time scale for the entrance section to return to a new equilibrium after a change in basin surface area is presented. To illustrate its practical use, the Escoffier method is applied to the Frisian Inlet before and after basin reduction. In 1969, the basin area and tidal prism were reduced by approximately 30%. Based on the Escoffier method, the original equilibrium cross-sectional area of 22,000 m 2 is expected to reduce to 15,500 m 2. The adaptation time scale is estimated to be 30 years. Even after basin reduction, the inlet remains very stable with S=31 and P/ V=585.

A GEM-TPC prototype with low-noise highly integrated front-end electronics for linear collider studies

Connected to the linear collider project, studies on the readout of time projection chambers (TPCs) based on the gas electron multiplier (GEM) are ongoing. Higher granularity and intrinsically suppressed ion feedback are the major advantages of this technology. After a short discussion of these issues, we present the design of a small and very flexible TPC prototype, whose cylindrical drift volume can be equipped with endcaps of different gas detector types. An endcap with multi-GEM readout is currently set up and successfully operated with a low-noise highly integrated front-end electronics. We discuss results of measurements with this system in high intensity particle beams at CERN, where 99.3 /spl plusmn/ 0.2 % single-pad-row efficiency could be achieved at an effective gain of 2.5 /spl times/ 10/sup 3/ only, and spatial resolutions down to 63 /spl plusmn/ 3 /spl mu/m could be demonstrated. Finally, these results are extrapolated to the high magnetic field in a linear collider TPC.

Leaky Valves in Littoral Sediment Budgets: Loss of Nearshore Sand to Deep Offshore Zones via Chutes in Barrier Reef Systems, Southeast Coast of Florida, USA

The decrease in longshore sediment volumes from north to south, calculated for littoral cells between inlets, indicates significant loss from the littoral drift system along the Florida east coast or localized deposition. The decrease in littoral drift volume from about 490,000 m3 of sediment over a distance of about 550 km (average diminution rate of about 890 m3 km−1) was traditionally accounted for in terms of alongshore deposition and some unknown degree of speculated offshore transport. With the application of laser airborne depth sounding (LADS) technology to bathymetric survey in southeast Florida (2001–2003), recognition of detailed bottom topography became possible for the first time. Significant in this regard was the bathymetric display of macro- and mesoscale morphological features that showed areal continuity of sandy bottoms and the prominent but disjunctive occurrence of relict barrier coral reef tracts that line the shelf edge. Identification of gaps in the line of barrier reefs showed pathways of cross-shore sediment transport from the inner shelf to offshore beyond the shelf edge. Diabathic sediment transport through these reef gaps robs the littoral sediment package by allowing the chuting of sediments during high energy events or when the backreef flats over fill with sand. The reef gaps are thus leaky valves where littoral sediments are periodically chuted offshore and lost from the littoral drift system.

Time projection chambers (TPC) in heavy ion experiments

In this paper the performance of TPCs in heavy ion experiments in terms of tracking and particle identification via dE/dx is reviewed. The principle of operation - drift, readout chambers and front end electronics, is illustrated. A few of the TPCs used are presented, along with a short description of the experiments. 1 TPC working principle A TPC is a three-dimensional almost continuous track- ing detector. It also provides information on the specific energy loss, dE/dx, of the particles traversing the drift volume. A TPC can be divided into three main parts: - The drift volume - The readout chambers - The readout electronics The charged particles produced in the collision pass through a gas mixture in the drift volume and release elec- trons from the gas atoms. These electrons drift in an ex- ternal electric field to the readout chambers. The drifting electrons initiate avalanches in the high fields at the an- ode wires providing an amplification. The electron cloud disappear immediately. The positive ions created in the avalanche induce a temporary image charge on the read- out pads which disappears as the ions move away from the anode wire. The image charge is measured by the readout electronics.

Fabrication of GEM Detector and X-ray Image Acquisition Based upon its Scintillation Lights

The gas electron multiplier (GEM), placed in the drift volume of a conventional gas detector, is a conceptually simple device for producing a large gas gain by concentrating the drift electric field over a very short distance to the point that electron avalanching occurs. This device consists of a thin insulating foil of several tens of jum in thickness, covered on each side with a thin metal layer, with tiny holes, usually 100 |um or less in diameter, and with a spacing of 100-200 Jim through the entire foil, perforated by using chemical etching or high-powered laser beam technique. In this study, we have investigated its operating properties with various experimental conditions and demonstrated the possibility of using this device as a digital X-ray imaging sensor, by acquiring X-ray images based upon the scintillation lights of the GEM with a standard CCD camera.

The concept of drift and its application to multiphase and multibody problems.

The concept of drift is built around understanding how a rigid body moving in a straight line distorts a material sheet in an unbounded perfect fluid. As the body moves from infinity through a material sheet, which is initially perpendicular to the direction of translation of the body, the sheet is permanently distorted. Darwin showed that the 'drift' volume, D(f), formed between the distorted and undistorted sheet is equal to C(m)V, where the added-mass coefficient, C(m), characterizes the shape of the body whose volume is V. Darwin's result is important for two reasons: first, it provides a means of quantifying how dyed fluid is transported from one place to another and dispersed; second, it provides a fundamental Lagrangian coordinate system to study inhomogeneous inviscid problems. The aim of this article is to review Darwin's contribution to fluid mechanics. By drawing on recent experimental measurements of drift and the drift volume, we aim to demonstrate how Darwin's drift concept has developed and to describe its broader significance for multiphase and multibody problems.

Effective generation of electron beams in an abnormal discharge with increased photoelectron emission from a cathode

An abnormal discharge is realized in which electron beams with energies in a kiloelectronvolt range are generated at an efficiency of η∼1. The results are explained within the framework of a photoelectron discharge model. A transition to this mechanism is possible due to a significant increase in the power of self-illumination from a large electron beam drift volume. The passage to a discharge with predominant photoemission leads to a decrease in the cathode potential fall region, a drop in the ion current to the cathode, and an increase in the efficiency.

Fluid displacement by Stokes flow past a spherical droplet

The concept of 'drift', which has been exploited in many high Reynolds number and inviscid flow problems, is here applied to examine transport by a spherical viscous droplet (of radius a) moving in a Stokes flow.In an unbounded flow, the velocity in the direction of translation of a spherical droplet is positive everywhere because streamlines, in the fluid frame of reference, 'close' at infinity. Fluid particles are displaced a positive distance, X, forward, which is expressed in terms of the initial distance from the stagnation streamline rho(0). Asymptotic expressions are developed for X in the limits of rho(0)/a much less than 1 and much greater than 1. The nature of the singularity of the centreline displacement changes from O(-a log(rho(0)/a)) to O(a(2)/rho(0)) as the viscosity of the droplet, compared to the ambient fluid, increases. By employing a mass-conservation argument, asymptotic expressions are calculated for the partial drift volume, D-p, associated with a circular material surface of radius rho(m) which starts far in front of a droplet that translates a finite distance. Since the velocity perturbation decays slowly with distance from the droplet, D-p tends to become unbounded as rho(m) increases, in contrast to inviscid flows.The presence of a rigid wall ensures that the velocity perturbation decays sufficiently rapidly that fluid particles, which do not lie on the stagnation streamline, are displaced a finite distance away from the wall. The distortion of a material surface lying a distance h(L) above a wall, by the droplet, starting a distance h(S) from the wall and moving away, is studied. The volume transported away from the wall, calculated using a multipolar flow approximation, is D-p = pih(L)(2)a(3lambda + 2)/(lambda + 1), and is weakly dependent on the starting position of the droplet, in accordance with numerical results. When the material surface is close to the wall (h(L)/a < 1), the volume transported away from a wall is significantly smaller than for inviscid flows because the no-slip condition on the rigid wall tends to inhibit 'scouring'. When the material surface is far from the wall (h(L)/a much greater than 1), the viscously dominated flow transports a larger volume of fluid away from the wall because the flow decays slowly with distance from the droplet.These results can be generalized to arbitrarily shaped bodies, since the transport processes are dominated by the strength of the Stokeslet. The effect of boundaries and inertia on fluid transport processes is briefly discussed.

Characteristics and Growth of a Snowdrift in Arctic Alaska, U.S.A.

In arctic Alaska, 15% of the total winter snowpack is contained in large drifts. Stratigraphic sections reveal that these can form during as few as five weather events during winter, while comparison of stratigraphy and weather records show that significant deposition (up to 43% of the total drift volume) can occur during a single event of short duration (<72 h). Based on three years of wind, snowfall, and snow transport records, a set of rules was developed for predicting when periods of drift growth would occur. The rules were: 10-m wind speed >5.3 m s−1 for at least 3 h, wind direction within 30° of the normal to drift trap axis, and recent snowfall available for transport. When used, these rules successfully identified all drift-growth events, plus a few “extra” events that did not contribute substantially to drift growth. The extra events were invariably periods when there was sufficient wind to move snow, but insufficient snow for transport. In arctic Alaska drift size currently appears to be limited by precipitation rather than wind, leading us to speculate that an increase in precipitation could increase drift size and intensify the ecological, hydrological, and climatic impact of drifts on this arctic system.

First observation of 140-cm drift ionizing tracks in the ICARUS liquid-argon TPC

This is a short note to acknowledge the successful operation of a 140-cm drift liquid argon TPC built in the framework of the ICARUS experiment. We show few cosmic muon tracks crossing the whole drift volume from the wire planes to the cathode. Data were taken at drift fields of 450 and 500 V/cm.

Longitudinal dispersion by bodies fixed in a potential flow

We examine tracer dispersion by the potential flow through a random array of rigid bodies fixed relative to a mean flow. Both Darcy flow through permeable bodies and inviscid irrotational flow past impermeable bodies are treated within one theoretical framework. The variation of the longitudinal dispersivity with body shape and permeability κ is examined for the case of high Peclet number, Pe . In the absence of diffusive effects, the longitudinal dispersivity D xx (where the mean flow is parallel to the x –axis) is calculated by tracing the evolution of a material surface advected by the mean flow and distorted by the array of bodies. For a random array of identical bodies of volume V and low volume fraction α, D xx = α | D f | UL / V . The drift volume, D f , is defined as the volume between the final and initial position of a material surface distorted by a single body moving in an unbounded flow, and L is the length–scale characterizing the associated longitudinal displacement of the surface. The variation of D xx with permeability is illustrated by considering permeable cylinders and spheres, and the effect of body shape on dispersion is illustrated by considering impermeable spheroids. The longitudinal dispersivity arising from the flow past impermeable bodies is D xx = α C xx UL , where C xx is the added–mass coefficient characterizing the mean flow around the body. This indicates that bluff bodies enhance longitudinal dispersion by promoting the longitudinal stretching of fluid elements. For Darcy flow through bodies of low permeability, the longitudinal dispersivity is Caligraphic D xx α( C xx + 1) UL . The length–scale L , and thus D xx, is singular as κ→ 0, owing to the long retention time of fluid within the bodies. For highly permeable two–dimensional bodies, Caligraphic D xx = α( C yy + 1) UL , where C yy is the added–mass coefficient characterizing the flow around an impermeable body moving parallel to the y –axis. Consequently, dispersion by highly permeable bodies is enhanced when the bodies are slender, in contrast to the low–permeability limit. The influence of finite tracer diffusivity on longitudinal dispersion is demonstrated to make a negligible contribution when κ< 0 provided Pe ≫ max (1, 1/κ) and for impermeable bodies provided Pe ≫ 1. When Pe ≪ 1/κ, the longitudinal dispersion is dominated by diffusive effects and D xx = O (α U 2 a 2 / D 1).

ARIANNA: the Icarus experiment readout module

Icarus detector is a liquid Argon Time Projection Chamber that requires continuous signal recording for each channel to provide three dimensional images of any ionizing event. A complete drift volume imaging of the next 600 ton module will result in 1.15 Gbit, with a data rate of 1.15 Tbit/s. The collected data can be highly reduced by recognizing Regions Of Interest (ROI) of the signal by means of a custom hit finding unit (DAEDALUS) working pipelined in the data acquisition path. DAEDALUS is an ASIC that implements an algorithm developed for hit detection and proven to be very efficient both on real and on simulated data. Since only ROI's are saved in memory and contiguous regions can be correlated to enhance detector self triggering capability, a high efficiency zero skipping is obtained in real time. A VME board hosting 16 Icarus digital channels has been designed and built as a demonstrator for functionality and performance test. The board, named ARIANNA, and DAEDALUS chip are here presented in detail.

Fluid displacement by high Reynolds number bubble motion in a thin gap

The fluid displacement associated with the injection and subsequent translation of high Reynolds number bubbles in a thin gap is examined experimentally, and compared with a theoretical model based on a two-dimensional inviscid flow calculation. In the experiments, air bubbles are injected and rise through an aqueous solution bound in a thin gap. Particular attention is given to the parameter regime characterised by the steady rectilinear motion of oblate elliptical or elliptical cap bubbles which transport a closed volume of fluid which trails the bubble in the form of a stable primary wake, and by laminar flow in the suspending fluid. The fluid displacement is measured by digitally tracking either particles suspended in the fluid, or the distortion of an initially horizontal fluid–fluid interface. While the fluid transport associated with the narrow region of viscous influence, or secondary wake, trailing the bubble is observed to contribute to the total fluid displacement over long times, its contribution is minimized by the influence of the channel walls. We thus focus on the fluid displacement associated with the irrotational component of the flow, which is described in terms of two components: a positive “drift” component which is localized near the point of crossing, and a negative “reflux” component required by continuity in a bounded domain. The experimental observations confirm a number of theoretical predictions concerning the fluid displacement accompanying high Reynolds number bubble motion. At distances greater than half the channel width from the point of injection, both the injection-induced displacement and the reflux are spread uniformly across the channel width. The reflux amplitude depends on the size of the primary wake, the drift volume and the channel width. The drift volume does not depend on the detailed shape of the bubble and wake or on the channel width, but is uniquely set by the cross-sectional area of the compound body composed of bubble plus wake. The shape of a distorted material surface depends weakly on the compound body shape, and becomes more peaked as the compound body becomes more oblate. This indicates that the presence of a primary wake adjoining a bubble will influence the longitudinal dispersion rather than the total drift volume. The relevance of this study for the analogous three-dimensional problem is discussed, and a heuristic model of mixing by high Reynolds number bubbles in a bounded domain is developed. The importance of fluid transport in the secondary wake, which was neglected in the theoretical model, is discussed in detail.

Displacement of inviscid fluid by a sphere moving away from a wall

We develop a theoretical analysis of the displacement of inviscid fluid particles and material surfaces caused by the unsteady flow around a solid body that is moving away from a wall. The body starts at position hs from the wall, and the material surface is initially parallel to the wall and at distance hL from it. A volume of fluid Df+ is displaced away from the wall and a volume Df- towards the wall. Df+ and Df- are found to be sensitive to the ratio hL/hs. The results of our specific calculations for a sphere can be extended in general to other shapes of bodies.When the sphere moves perpendicular to the wall the fluid displacement and drift volume Df+ are calculated numerically by computing the flow around the sphere. These numerical results are compared with analytical expressions calculated by approximating the flow around the sphere as a dipole moving away from the wall. The two methods agree well because displacement is an integrated effect of the fluid flow and the largest contribution to displacement is produced when the sphere is more than two radii away from the wall, i.e. when the dipole approximation adequately describes the flow. Analytic expressions for fluid displacement are used to calculate Df+ when the sphere moves at an acute angle α away from the wall.In general the presence of the wall reduces the volume displaced forward and this effect is still significant when the sphere starts 100 radii from the wall. A sphere travelling perpendicular to the wall, α = 0, displaces forward a volume Df+(0) = 4πa3hL/33/2hS when the marked surface starts downstream, or behind the sphere, and displaces a volume Df+(0) ∼ 2πa3/3 forward when it is marked upstream or in front of the body. A sphere travelling at an acute angle away from the wall displaces a volume Df+(α) ∼ Df+(0) cos α forward when the surface starts downstream of the sphere. When the marked surface is initially upstream of the sphere, there are two separate regions displaced forward and a simple cosine dependence on α is not found.These results can all be generalized to calculate material surfaces when the sphere moves at variable speed, displacements no longer being expressed in terms of time, but in relation to the distance travelled by the sphere.

Position sensitive x-ray detector OD-3

A fast one-coordinate x-ray detector of a new design aimed for angular measurements in diffraction experiments was developed in BINP. The detector is based on a multiwire proportional chamber with x-ray absorption drift volume. It allows acceptance of photons in the energy range from 6 keV to 20 keV with a maximum rate of 10 MHz/detector and coordinate resolution about 0.1 mm (rms) in linear scale. The first OD-3 chamber has a 0.4-mm-thick Be inlet window 200 mm x 10 mm, a photoabsorbtion length of 50 mm, and a parallax-free cathode structure for angles up to ±15 degrees at variable focal length (from 300 mm to 450 mm without any modification and to infinite at cathode plane replacement). The first tests of the detector at synchrotron radiation beamline 5-b VEPP-3 and with a x-ray tube show a good performance. The detector construction specifics and test results will be discussed in the report.

The city of Tyre, Lebanon and its semi-artificial tombolo

The sedimentological history of the peninsular city of Tyre, located on the southern coast of Lebanon, reflects the political events surrounding Alexander the Great's conquest of the East (332 B.C.E.). Like many other Phoenician settlements, the city was originally situated on a small, relict rocky islet, but was later connected to the mainland by an artificial causeway constructed by Alexander's troops. As a result of the causeway construction, a gigantic tombolo formed, composed of at least 10 million m3 of sediment, mostly sand. Calculations based on the present size of the land tombolo of Tyre show that the average regional yearly volume of sand drift from the south and the north for the past 2300 years was approximately 4000 m3. If the present composition of high carbonate tombolo sands is representative of the entire sand body of the tombolo, about two thirds of the mass originates from nearby beaches which formed as a result of the erosion of the Pleistocene carbonate sandstone known as “Hajar Ramli.” © 1996 John Wiley & Sons, Inc.